In addition to electric charge, electrons have physical quantities called spins, which are the origin of magnetism. That is, when the electron spins inside a substance are deviated in a certain direction, that is, when spin polarization occurs, the substance has magnetism.
Hereinafter, the distribution of charged particles having upward spins and charged particles having downward spins is called “spin distribution,” and that the spin distribution is deviated (not uniform) is called “spin polarization.” Moreover, the deviation of the ratio of the upward to the downward spins included in the charged particle flux is called a “spin polarization degree.”
As for electron beams, a spin-polarized electron beam in which the ratio of the spins included in the electron beam is deviated to one side is utilized as a means for microscopically examining the magnetism of a substance. As for the spin polarization degree, for example, the polarization degree is 100% (completely polarized) when all the spins are upward (or downward) and 0% (not polarized at all) when the numbers of the upward and downward spins are the same.
Recently, a spin-polarized electron beam using a superlattice of GaAs/GaAsP as an electron source have particularly attracted attention because the spin polarization degree thereof exceeds 90% (conventionally about 50%) and the like. New findings are expected to be obtained by irradiating a sample with the spin-polarized electron beam having such a spin polarization degree to observe and measure the sample.
For a transport optical system of this spin-polarized electron beam, an electrostatic lens and a magnetic lens for ordinary electron beams are used, and a spin rotator is also used for rotation in a spin polarization direction. Herein, the transport optical system refers to a system which transports particles generated from a particle beam source, such as electrons, to a measuring or processing sample.
When the spin-polarized electron beam passes through, for example, a nonuniform magnetic field, dispersion occurs in a Larmor rotation angle due to the magnetic field, and thus the polarization degree becomes small. For example, since nonuniform magnetic fields are distributed at the entrance and exit of a magnetic lens and the like often used in the transport optical system, there is a high possibility that the spin polarization degree becomes small as described above. However, currently, there is no transport optical system which intentionally adjusts or increases the spin polarization degree.
As described above, there has been no report on a transport optical system which adjusts the magnitude of the spin polarization degree or a transport optical system which adjusts the trajectories of the electrons depending on the spins.
Note that PTL 1 and 2 disclose detectors capable of highly efficiently decomposing the magnetic moments possessed by charged particles. Moreover, NPL 1 discloses a spin-polarized low energy electron microscopy (SPLEEM) which irradiates a magnetic material with a spin-polarized electron beam to measure the intensity of the reflection electrons thereof.